1. Field of the Invention
The present invention generally relates to a method of manufacturing an optical system, an optical system and a method of manufacturing an optical element. In particular, the present invention involves obtaining position or shape information using measuring light diffracted at holograms.
2. Brief Description of Related Art
Generally, a performance of an optical system is determined by a quality of its optical components, such as lenses and mirrors, comprised by the system, and by an accuracy of an alignment of the optical components relative to each other.
Typically, the optical elements are made of a glass or other suitable material, and their optical surfaces are processed to have a surface shape corresponding to a specification of the optical system. Herein, it is necessary to compare the shape of the processed optical surface with its target shape according to the design, and to determine differences between the processed actual surface and the target surface. The optical surface may then be further processed at those portions where differences between the actual surface and the target surface exceed e.g. predetermined thresholds.
Thereafter, each of the finished optical elements is attached to a mounting frame made of metal or other suitable material, wherein the mounting frame provides mechanical attachment means, such as flanges, through-holes and others. Thereafter, the optical system is assembled by attaching the respective mounting frames to each other in such a way that positions, such as distances and orientations, of the optical elements relative to each other conform with the specification of the optical system.
Thus, the manufacture of the optical system comprises manufacture of optical elements, manufacture of mounting frames, mounting the optical elements on the respective mounting frames and aligning the mounting frames relative to each other. Especially in the field of photolithography the trend to ever smaller structures of the devices which are to be manufactured places ever higher demands on the quality of the optical imaging systems, and thus on the manufacture of the optical elements and the alignment of the optical elements relative to each other.